FIELD OF THE INVENTION
This invention relates in general to gas detection devices and in particular to a new useful method and apparatus for detecting the reaction of gases to an indicator.
The invention particularly concerns a process for measuring flat discoloration zones on an indicator substrate by which a movable indicator substrate is transported into a measuring position and there treated with a gaseous medium, and the discoloration zone of the gas-treated indicator section is measured electro-optically and a measured value is determined in a measuring cycle by an electronic evaluating instrument.
A similar process is discussed in the DE/OS No. 28 04 841. There, the mean concentration of a gas or a gas component in a gas mixture is determined by the electro-optical measurement of the discoloration of a reagent paper band. The discoloration of the gas-treated field is determined until a predetermined threshold value is reached and the reagent paper band is then moved always by one gas-treated field, the mean concentration of the gas can be determined from the number of gas-treated fields that are discolored during the total gas-treatment time.
In another, known process according to the DE/OS No. 24 07 224, the time of the discoloration elasped until reaching a predetermined threshold value is compared with a set retardation time. The regent paper band is moved after this time has elapsed. The mean concentration of the test gas can be determined for each time period during this time period.
A comparable state of the art is also described in the DE-Z Dragerheft 313, January to April 1979, in the report by W. Diehl, D. Gellendin, L. Grambow, K. K. Huneke and H. Zwintscher, "The Toxiwarn--a portable measuring and warning instrument for toxic gases". The construction of this instrument provides for the pressing of an indicator strip after it is rolled off a storage roll, against a gap in the outside wall of a measuring chamber, through which the gas to be tested flows. The diffuse reflection of a band section is untreated and one that is treated with gas is scanned by a system of a light source and a photo element. The concentration of the gas to be determined can be obtained from their recorded measurements. For the determination of the mean gas concentration over a time that can be selected at will, the obtained measurements are summed up and stored. The mean concentration during the measuring time period is obtained from the measurement integration and the time integration.
But the previously known processes does not meet all requirements with regard to the desired measuring dynamic and accuracy.